Hmmph, the same mistake I made last week, (in another forum).
[There *is* a form called Monolophosaurus, but I think it is from
Mongolia].

The correct name is Cryolophosaurus ellioti, and it is from
the Early Jurassic, or Latest Triassic.

>It seems to have a crest, like the hadrosaurs, which would have been> used for species-species interactions and mate attraction.

Like hadrosaurs, and like many other theropods.
[Dilophosaurus, Monolophosaurus, Carnotaurus, Abelisaurus
all have rather large crests, and many others, like Tyrannosaurus,
Albertosaurus, Allosaurus and so on, have small crests].

And, you are quite right - species specific interactions
are almost certainly the purpose of such crests.

> I THINK it is from the carnosaur group, but I'll have to check.

That my depend on what you mean by Carnosaur. According to the
paper in Science, is has features similar to both Tetanurans
(including Carnosauria sesu stricto) and Ceratosauria.

It seems to be most similar to "primitive" carnosaurs like
Gasosaurus and Yangchuanosaurus, although it might instead be
related to Abelisaurus or Megalosaurus.